People often need to establish voice and data communications with separate destinations at the same time. Prior art methods for obtaining such voice and data communication services include employing (a) Integrated Services Digital Network (ISDN) technology, which is an all digital technology that provides a user with two separate bearer (B) channels, each of which independently and simultaneously carries user information, so that one channel may carry voice while the other channel carries data; b) multiple "plain old telephone service" (POTS) lines; and c) data over voice modems, which carry a full POTS channel and a full data channel on a carrier frequency well above the highest POTS-channel frequency.
ISDN 1) is expensive to implement, 2) is not universally available, and 3) must be provisioned by the local exchange carrier (LEC). Multiple POTS lines are expensive and cumbersome to deal with. Each data over voice modem requires a) a dedicated modem in the central office, b) special conditioning of the local loop to the central office, and c) a limit on the loop length connecting the data over voice modem to the central office. These limitations arise because data over voice modems require additional bandwidth substantially beyond that which is available over a single POTS connection. In addition to the above-noted disadvantages, all the foregoing technologies must be provisioned for use ahead of time, resulting in their being inflexible and lacking portability. As a result, ISDN and data over voice service are not widely available.
Another prior art technology for providing a user with simultaneous voice and data communication service is employed in SVD modems. SVD modems are modems for use in providing simultaneous voice and data service within the bandwidth provided by a single POTS connection, i.e., a bandwidth of approximately 3200 hertz. Present SVD modems typically can provide a telephone quality voice channel and a data channel of up to 4800 bits per second simultaneously. Should the data channel not be in use, the quality of the voice channel is increased slightly. Similarly, if the voice channel is not in use, the speed of the data channel can be increased to 14.4 Kbits per second. (For a detailed description of exemplary technology used in SVD modems see patent application Ser. No. 08/076,505 filed Jun. 14, 1993 and assigned to the same assignee as the present invention.) One exemplary, commercially available SVD modem is the AT&T DataPort.RTM. 2001 modem. It is anticipated that future SVD modems will be more efficient, permitting an even higher rate of data transmission while the voice channel is in use.
Because SVD modems communicate over a single POTS channel, they can be attached to the large number of POTS subscriber telephone lines without any advanced provisioning. However, at present, SVD modems can only be used to provide point-to-point simultaneous voice and data service where the parties at each end of the POTS connection have an SVD modem, thereby limiting their usefulness.
In concurrently filed application Ser. No. 08/176,002 it is recognized that an improvement in providing simultaneous voice and data communications can be achieved by provisioning within the public switched telephone network one or more SVD modems that (a) can communicate with SVD modems of the network users over a single "plain old telephone service" (POTS) connection, and (b) can separate, and deliver to different destinations the voice and data channels received from an SVD modem. In order to deliver the received voice and data channels to different destinations, the voice and data channels may be routed separately and independently through the public switched telephone network. The SVD modems in the public switched telephone network can also combine voice and data traffic from separate sources for transmission together over a single POTS connection to a user's SVD modem.
In one exemplary system, an inter-exchange carrier (IXC), e.g., AT&T, provides a plurality of SVD modems arranged as a "modem pool". Callers may access the SVD modems of the pool, which constitutes a shared network resource, to obtain simultaneous voice and data service. To access the SVD modems of the pool, special dialing codes and an optional login procedure are employed. The voice and data channels of an SVD call from a caller are separated at the network side of the SVD modem pool, so that they may be routed to different destinations. After separation, the voice channel of the call is routed over the IXC's circuit switched network and the data channel of the call is carried over a packet network. The voice channel of the call (a) may be routed in the usual manner, e.g., (1) through a LEC, to a voiceband device, such as a telephone, answering machine, facsimile (fax) machine, or conventional modem, or (2) to a network based voiceband audio service; or (b) it may be routed to an SVD modem pool for possible combination with a data channel for delivery to an end-point subscriber who has an SVD modem. The data channel of the call may be routed over the packet network to (a) a host directly connected to the packet network, (b) a modem pool having conventional data only modems, or (c) an SVD modem pool for possible combination with a voice channel for delivery to the end-point subscriber who has an SVD modem.
A user whose SVD modem is connected to an SVD modem in the public switched network and who is not using both the voice and data channels provided by the SVD modem, may originate or receive calls on the unused channel.